Range using single-mode SFPs across multi-mode fiber

Thanks to all who responded to my clumsy first question (both on
matters of etiquette and technology). The group I work with (we are a
small project acting as a last mile provider) was in the midst of
deploying this solution when I posed the question. We put the single
mode Juniper SFPs (LX) on to a run of approximately 1670 meters. We
successfully established a 1G ethernet connection. Testing to date has
been meager, but shows that the link is viable. Under significant load
there is some minor packet loss. Since the link far exceeds the amount
of data it required, we have decided to continue using it.
Interestingly neither interface showed any physical errors.

Oliver Rothschild
Network Engineer III

Technically you should be using offset-launch "mode conditioning"
patch cords at each end when running LX over multimode fiber. I had
been lucky with not using them for many years on 62.5/125 (OM1)
multimode (and just started doing so again, albiet only for
OOB/non-production traffic use). I believe my longest link was/is
around 1 km.


How did you end up with a MM run this long? SX optics are only rated at
500 meters at best. Even with mode conditioning jumpers more the 1km is a
risk. I'm glad it held up during testing though. Just out of curiosity
did you purchase dark from a provider? Is it inside of a building?

Um.. check that.


"Typical transmission speed and distance limits are 100 Mbit/s for
distances up to 2 km (100BASE-FX
<https://en.wikipedia.org/wiki/100BASE-FX>), 1 Gbit/s to 220--550 m
(1000BASE-SX <https://en.wikipedia.org/wiki/1000BASE-SX>), and 10 Gbit/s
to 300 m (10GBASE-SR

The old OM1 installations I used to work on started out as 10Mbit hubbed
ethernet links and on the odd occasion would run out to close to 2km
within a campus. They were progressively upgraded with the flow of:

10FX on 3Com Linkbuilder Kit
100FX on 3Com Corebuilder Kit and Allied Telesyn 100FX Media converters
1000SX on a variety of 3Com, Nortel and Cisco kit out to ~220m
1000LX via Mode-Conditioning out to ~900-1000m.

The OM1 only got retired when the distance was >900m or there was budget
to put new fibre on the run, in which case we ran SMF and rigged LX drivers.


In my case, it was installed for compatibility with FDDI, and used
mostly for 10BASE-FL and 100BASE-FX, which work up to 1 or 2km, until
we started using it for 1000BASE-LX.

I stand corrected, but I haven't dealt much with 100BASE-FX. I was just
talking in terms of 1G/10G.

Some idiot jumpered runs that existed between 3 different buildings. That person did not know about the 550m limit that we also follow.

Legacy 10baseFL/100baseFX/FDDI can run fairly long distances over OM1. In the past I've run 100baseFX over OM1 runs with multiple cross-connects, out to about 2 km.


The max limit for 100 base FX (100 Mbps Ethernet) is around 6600 feet. Many campus ductbank systems built in the 1990s when 10 and 100 Mbps Ethernet were the commodity speeds (before GiGE) used 62.5/125 MM fiber to connect buildings. It is not unusual to see long MM runs on campus facilities where 100 Mbps backbones once were the fastest speeds available.

In those days, apart from longhaul telco use, singlemode fiber was usually only run for closed circuit TV (CCTV) use in the campus environment, and in places where 1990s SM was run for CCTV it can still be used for longhaul laser sfps, which to me shows that SM is future proof. SM even makes sense in short runs as attenuators can be placed on the send/receive strands to reduce the dB so the optical receiver is not saturated.